Controllable damper systems have been proposed for a number of applications, including trucks, off-highway equipment, construction equipment, and automotive. Controllable dampers can provide continuous adjustment of the output force over a significant range, as opposed to passive systems which have unchangeable operating characteristics. Controllable fluid dampers, which are available in various types, are particularly advantageous because of the extremely fast response time. U.S. Pat. No. 5,277,281 to Carlson et al. which discloses a magnetorheological fluid damper. An electrophoretic fluid damper is disclosed in U.S. Pat. No. 5,018,606 to Carlson. U.S. Pat. No. 5,522,481 to Watanabe discloses an electrorheological fluid damper. These type dampers are controlled by changing the electric or magnetic field applied to a fluid whose apparent viscosity is responsive to the field.
One advantageous use for controllable dampers is in secondary suspension systems, for example, suspension systems for vehicle seats or cabs. Isolating the seat or cab from the vehicle frame to protect the operator from vibrations transmitted through the vehicle can improve the operator's ability to control the vehicle and may reduce vibrations experienced by the operator.
Commonly owned U.S. Pat. Nos. 5,652,704, entitled "Controllable Seat Damper System and Control Method Therefor" and 5,712,793, entitled "Control Method For Semi-Active Damper" disclose systems using a controllable fluid damper such as a magnetorheological (MR) type, in combination with vehicle suspension systems. In such a system, for example a seat suspension system, the system actively controls damping by sensing the seat position and the rate of change of the seat position and calculates an appropriate damping force based on a stored algorithm.
To install and operate controllable damper systems the kinematic parameters of the suspension system must be supplied to the control system. The parameters include, for example, the movement limits of the supported body (the maximum upper and lower positions) and the end stop limits (the positions at which increased damping is used to avoid sudden collision with a maximum or minimum position). These parameters are different for different suspension systems, for example, seats from different manufacturers.
The problem of determining the kinematic parameters is compounded for the installation of a controllable damper system in an existing vehicle. In addition to variations in the seat and suspension components, additional variations may be introduced by the person doing the installation of the damper system due to positioning of the sensors, and the like.
Any of these factors, in original or retrofit systems, can skew the expected values of the kinematic parameters. Controllable damper systems have accordingly, until now, required individual, manual calibration.
The present invention provides a method for the automatic calibration of a controllable damper system that avoids the problems of variation in suspension kinematics and facilitates damper system setup. The method according to the invention automatically performs steps to determine the positional parameters and preferably also calculates the end stop and other parameters. These values are stored for use by the damping control system.
The invention also allows for the re-calibration of an installed system, which may be needed when field parameters change, for example, after a repair is made to the suspension structure or the controllable damper system is switched to a new seat.
The method is particularly advantageous for damper systems as described in U.S. Pat. No. 5,652,704, and U.S. Pat. No. 5,712,783, the disclosures of which are incorporated herein by reference. In particular, the description below discusses a seat for a truck, however, the method of the invention may be employed with other controllable damping systems for other structures, such as with suspended vehicle cabs, and the like. The description herein is not meant to limit the invention to a truck seat damper.
According to the method of the invention, an initiation signal is received, which causes the calibration routine to activate. The system first checks that the initiation signal meets set criteria to confirm that calibration is intended. If the signal does not meet the criteria, the system takes default values or the last stored values for use by the damping control system. If the signal does meet the criteria, the system begins by automatically moving the seat first to a first position (preferably the upper maximum seat height position) and obtaining a first (upper) limit signal from a position sensor for that seat height position. The seat is then moved to a second position (preferably, the bottom minimum seat height position), and a second (lower) limit position signal is similarly obtained. From these two signal values, a position range may be calculated as an arithmetic difference between the values. Additionally, a center or neutral position value may also be determined, and the seat optionally may be moved to that position. The neutral position represents a preferred set position for the seat.
The system preferably also calculates end stop limits, which are position ranges near the extreme seat positions. The end stops are used as triggers to increase the damping to prevent the seat from colliding with the suspension structure at the end of the range of motion or bottoming out of the damper itself. The end stops are preferably calculated as a percentage of the complete range of motion, and for a truck seat, for example, may be set at 30% for the upper limit and 20% for the lower limit. The end stops are also used to limit the range of leveling available to the user for positioning the seat. Optionally, the end stops may be predetermined values.
The values measured and calculated by the system are stored for use by the damping control system, which completes the calibration routine.